This invention relates generally to a computer-controlled object-building process and apparatus and, in particular, to an improved process and apparatus for building a three-dimensional object in a layer-by-layer fashion.
Solid freeform fabrication (SFF) or layer manufacturing is a new rapid prototyping technology that builds an object layer by layer or point by point. This process begins with creating a Computer Aided Design (CAD) file to represent the image or drawing of a desired object. As a common practice, this CAD file is converted to a stereo lithography (.STL) format in which the exterior and interior surfaces of the object is approximated by a large number of triangular facets that are connected in a vertex-to-vertex manner. A triangular facet is represented by three vertex points each having three coordinate points: (x1,y1,z1,), (x2,y2,z2), and (x3,y3,z3). A perpendicular unit vector (i,j,k) is also attached to each triangular facet to represent its normal for helping to differentiate between an exterior and an interior surface. This object image file is further sliced into a large number of thin layers with the contours of each layer being defined by a plurality of line segments connected to form polylines. The layer data are converted to tool path data normally in terms of computer numerical control (CNC) codes such as G-codes and M-codes. These codes are then utilized to drive a fabrication tool for building an object layer by layer.
This SFF technology enables direct translation of the CAD image data into a three-dimensional (3-D) object. The technology has enjoyed a broad array of applications such as verifying CAD database, evaluating design feasibility, testing part functionality, assessing aesthetics, checking ergonomics of design, aiding in tool and fixture design, creating conceptual models and sales/marketing tools, generating patterns for investment casting, reducing or eliminating engineering changes in production, and providing small production runs.
A commercially available system, fused deposition modeling (FDM) from Stratasys, Inc. (Minneapolis, Minn.), operates by employing a heated nozzle to melt and extrude out a nylon wire or wax rod. The starting material is in the form of a rod or filament that is driven by a motor and associated rollers to move like a piston. The front end, near a nozzle tip, of this piston is heated to become melted; the rear end or solid portion of this piston pushes the melted portion forward to exit through the nozzle tip. The nozzle is translated under the control of a computer system in accordance with previously sliced CAD data. The FDM technique was first disclosed in U.S. Pat. No. 5,121,329 (1992), entitled xe2x80x9cApparatus and Method for Creating Three-Dimensional Objects,xe2x80x9d issued to S. S. Crump. A more recent patent (U.S. Pat. No. 5,738,817, April 1998, to Danforth, et al.) reveals a fused deposition process for forming 3-D solid objects from a mixture of a particulate composition dispersed in a binder. The binder is later burned off with the remaining particulate composition densified by re-impregnation or high-temperature sintering. Other melt extrusion-type processes include those disclosed in Valavaara (U.S. Pat. No. 4,749,347, June 1988), Masters (U.S. Pat. No. 5,134,569, July 1992), and Batchelder, et al. (U.S. Pat. No. 5,402,351, 1995 and U.S. Pat. No. 5,303,141, 1994). These melt extrusion based deposition systems are known to provide a relatively poor part accuracy. For instance, a typical FDM system provides an extruded strand of 250 to 500 xcexcm, although a layer accuracy as low as 125 xcexcm is achievable. The accuracy of a melt extrusion rapid prototyping system is limited by the orifice size of the extrusion nozzle, which cannot be smaller than approximately 125 xcexcm in real practice. Otherwise, there would be excessively high flow resistance in an ultra-fine capillary channel. Such a system, however, can provide a relatively fast deposition rate provided a larger-diameter nozzle orifice is utilized.
In U.S. Pat. No. 4,665,492, issued May 12, 1987, Masters teaches part fabrication by spraying liquid resin droplets, a process commonly referred to as Ballistic Particle Modeling (BPM). The BPM process includes heating a supply of thermoplastic resin to above its melting point and pumping the liquid resin to a nozzle, which ejects small liquid droplets from different directions to deposit on a substrate. Sanders Prototype, Inc. (Merrimack, N.H.) provides inkjet print-head technology for model making. Multiple-inkjet based rapid prototyping systems are available from 3D Systems, Inc. (Valencia, Calif.). Inkjet printing involves ejecting fine polymer or wax droplets from a print-head nozzle that is either thermally activated or piezo-electrically activated. The droplet size typically lies between 30 and 50 xcexcm, but could go down to 13 xcexcm. This implies that inkjet printing offers a high part accuracy. However, building an object point-by-point with xe2x80x9cpointsxe2x80x9d or droplets as small as 13 xcexcm could mean a slow build rate.
In a series of U.S. patents (U.S. Pat. No. 5,204,055, April 1993, U.S. Pat. No. 5,340,656, August 1994, U.S. Pat. No. 5,387,380, February 1995, and U.S. Pat. No. 5,490,882, February 1996), Sachs, et al. disclose a 3-D printing technique that involves using an ink jet to spray a computer-defined pattern of liquid binder onto a layer of uniform-composition powder. The binder serves to bond together those powder particles on those areas defined by this pattern. Those powder particles in the un-wanted regions remain loose or separated from one another and are removed at the end of the build process. Another layer of powder is spread over the preceding one, and the process is repeated. The xe2x80x9cgreenxe2x80x9d part made up of those bonded powder particles is separated from the loose powder when the process is completed. This procedure is followed by binder removal and metal melt impregnation or sintering. Again, ejection of fine liquid droplets to bond a large area of powder particles could mean a long layer-building time.
The selected laser sintering or SLS technique (e.g., U.S. Pat. No. 4,863,538) involves spreading a full-layer of powder particles and uses a computer-controlled, high-power laser to partially melt these particles at desired spots. Commonly used powders include thermoplastic particles or thermoplastic-coated metal and ceramic particles. The procedures are repeated for subsequent layers, one layer at a time, according to the CAD data of the sliced-part geometry. The loose powder particles in each layer are allowed to stay as part of a support structure. The sintering process does not always fully melt the powder, but allows molten material to bridge between particles. Commercially available systems based on SLS are known to have several drawbacks. One problem is that long times are required to heat up and cool down the material chamber after building. In addition, the resulting part has a porous structure and subsequent sintering or infiltration operations are needed to fully consolidate the part.
U.S. Pat. No. 5,555,481, issued on Sep. 10, 1996 to Rock and Gilman, discloses a powder-based layer manufacturing method that is capable of creating parts with spatially controlled material compositions. This technique involves producing parts using two distinct classes of materials. According to this method, a first class material and a second class material are deposited on a surface wherein the first class material forms a three-dimensional shape defined by the interface between the first class material and the second class material. The first class material is unified by subsequent processing such as sintering or fusion-and-solidification, which is followed by removing the second class material from the three-dimensional part made up of first class material. The second class material plays the basic role of serving as a support structure. Upon completion of the deposition procedure for all layers, the green object which has been compacted but not yet unified is highly delicate and fragile, prone to shape changes during subsequent handling. The final unification procedure tends to involve dimensional or shape changes in a part, thereby compromising the part accuracy. For instance, sintering of ceramic or metallic particles is known in the field of powder technology to involve large shrinkage. Solidification of a crystalline material (polymer, metal, and ceramic) from the melt state to the solid state are normally attendant with a large volume change. Since these geometry changes are allowed to occur at the end of the part building process, it is extremely difficult to exercise any corrective action to ensure the part accuracy.
Most of the prior-art layer manufacturing techniques have been largely limited to producing parts with homogeneous material compositions. Furthermore, due to the specific solidification mechanisms employed, many other techniques are limited to producing parts from specific polymers. For instance, Stereo Lithography and Solid Ground Curing (SGC) rely on ultraviolet (UV) light induced curing of photo-curable polymers such as acrylate and epoxy resins. The SGC system uses UV-curable acrylate photo polymer and a photo-masking technique. A mask generator produces a negative image of the desired layer cross-section on a glass mask plate. A thin layer of liquid photo polymer is spread across the object-supporting platform and a strong UV light is allowed to pass through the transparent portions of the mask to selectively cure the polymer in these desired regions. Uncured resin is then removed by a vacuum cleaner and wax is spread across the layer to fill in any gaps (left behind by the removed resin, for instance). After the wax is solidified it is then machined flat to provide support for the cured resin. A major disadvantage of this technique is that it produces excessive waste of resin and wax. Additionally, the system requires attended operation and is, therefore, not considered to be a fully automated fabrication technique.
Either droplet deposition or melt extrusion method alone does not meet the two critical requirements imposed upon a rapid prototyping (RP) system: speed and accuracy. For instance, liquid droplet ejection features high accuracy but low speed, while melt extrusion features relatively higher speed but much lower accuracy.
Additionally, most of the current RP systems are not effective in varying the colors of an object from layer to layer and from spot to spot. In principle, a melt extrusion system can change the color of an extruded strand of liquid by feeding a material with a different color. But, it would take a relatively long time for an extrusion device to dispense the new color material after a new color is added. The extruder chamber and nozzle have a channel of finite length in which undesirable mixing of colors can occur. Color adjustments can be made much more readily with droplet deposition methods. Two-dimensional color inkjet printing is now commonplace. Color inkjet printers are found in an ever-increasing number of homes and offices worldwide. However, rapid prototyping technology developers have not taken full advantage of color printing technology. The current droplet deposition based RP systems still lack the capability to freely adjust the color so that an object with a desired color pattern can be made under the control of a computer. Yamane, et al. (U.S. Pat. No. 5,059,266, October 1991 and U.S. Pat. No. 5,140,937, August 1992) disclose a droplet jetting system for fabricating 3-D objects from photosetting or thermosetting resins. Droplet jetting from other types of material was not addressed in these two patents. The possible need to build a support structure for any un-supported feature in a given object was overlooked.
In U.S. Pat. No. 5,015,312, issued May 14, 1991, Kinzie discloses a method and apparatus for constructing a 3-D xe2x80x9csurface xe2x80x9d of predetermined shape and color from a length of sheet material. This method begins by making a series of color profiles along one side (top or bottom surface, but not the edge) of the sheet material in sequence. Each color profile corresponds in shape and color to the shape and color of a different cross section of the surface to be constructed. Areas on the sheet material outside of the profiles are then removed and discarded so as to leave a series of unconnected planar elements. Each planar element has an edge shape or outline corresponding to a cross-section of the surface with the color profile itself forming at least a color border or margin on the surface of its respective planar element around the edge. These individual planar elements are then glued together in a proper sequence to form a xe2x80x9claminatedxe2x80x9d structure. When viewed, the entire surface of this structure appears to be colored even though the color is applied only along one side (top or bottom surface, but not along the edges) of individual planar elements. This method does provide a variable multi-color exterior surface of an object. This layer-subtractive method, however, pays little attention to the formation of interior features (e.g., shape and dimension of a channel) of a 3-D object. A useful prototype requires the formation of more than just its outside surface. Further, the final stacking-up and lamination procedures must be carried out manually and the creation of color profiles on each layer is a lengthy procedure. Hence, this process is expected to be slow and labor intensive. Furthermore, since colors do not appear on the edge surface of a cross section, any portion of the structure composed of uniform-cross section layers will not exhibit a desirable color perception.
In U.S. Pat. No. 5,514,232, issued May 7, 1996, Burns discloses a method and apparatus for automatic fabrication of a 3-D object from individual layers of fabrication material having a predetermined configuration. Each layer of fabrication material is first deposited on a carrier substrate in a deposition station. The fabrication material along with the substrate are then transferred to a stacker station. At this stacker station the individual layers are stacked together, with successive layers being affixed to each other and the substrate being removed after affixation. One advantage of this method is that the deposition station may permit deposition of layers with variable colors or material compositions. In real practice, however, transferring a delicate, not filly consolidated layer from one station to another would tend to shift the layer position and distort the layer shape. The removal of individual layers from their substrate also tends to inflict changes in layer shape and position with respect to a previous layer, leading to inaccuracy in the resulting part.
In U.S. Pat. No. 5,301,863 issued on Apr. 12, 1994, Prinz and Weiss disclose a Shape Deposition Manufacturing (SDM) system. The system contains a material deposition station and a plurality of processing stations (for mask making, heat treating, packaging, complementary material deposition, shot peening, cleaning, shaping, sand-blasting, and inspection). Each processing station performs a separate function such that when the functions are performed in series, a layer of an object is produced and is prepared for the deposition of the next layer. This system requires an article transfer apparatus, a robot arm, to repetitively move the object-supporting platform and any layers formed thereon out of the deposition station into one or more of the processing stations before returning to the deposition station for building the next layer. These additional operations in the processing stations tend to shift the relative position of the object with respect to the object platform. Further, the transfer apparatus may not precisely bring the object to its exact previous position. Hence, the subsequent layer may be deposited on an incorrect spot, thereby compromising part accuracy. The more processing stations that the growing object has to go through, the higher the chances are for the part accuracy to be lost. Such a complex and complicated process necessarily makes the over-all fabrication equipment bulky, heavy, expensive, and difficult to maintain. The equipment also requires attended operation.
Therefore, an object of the present invention is to provide a layer-additive process and apparatus for producing an object with improved build rate and part accuracy.
Another object of the present invention is to provide a computer-controlled process and apparatus for producing a multi-color 3-D object on a layer-by-layer basis.
It is a further object of this invention to provide a computer-controlled object-building process that does not require heavy and expensive equipment.
It is another object of this invention to provide a process and apparatus for building a CAD-defined object in which the color pattern can be predetermined.
Still another object of this invention is to provide a layer manufacturing technique that places minimal constraint on the range of materials that can be used in the fabrication of a 3-D object.
The Process
The objects of the invention are realized by a process and related apparatus for fabricating a three-dimensional object on a layer-by-layer basis. Basically, the process comprises co-deposition of ejected liquid droplets and solid powder particles at predetermined proportions to build an object, preferably under the control of a CAD computer. Both liquid droplets and solid powders can be selected from a wide range of materials. Liquid droplets may also contain desired color dyes for building a multi-color object.
One embodiment of the present invention is a process for building a 3-D object in a layer-by-layer fashion. The process comprises the steps of:
(a) operating a material deposition sub-system which comprises (1) a multiple-channel droplet deposition device for supplying multiple liquid compositions and ejecting droplets of selected liquid compositions on demand and (2) a powder dispensing device to deposit fine solid particles on demand so that the deposited liquid droplets and solid particles are well mixed at predetermined proportions;
(b) providing an object-supporting platform in a close working vicinity of the material deposition sub-system to receive the liquid droplets and solid powder particles therefrom; and
(c) during the droplet ejecting and powder dispensing process, moving the material deposition sub-system and the object platform relative to one another in an X-Y plane defined by first (X-) and second (Y-) directions and in a third or Z-direction orthogonal to the X-Y plane to form the liquid droplets and solid particles (collectively referred to as deposition materials) into a three dimensional object. Liquid compositions may comprise selected dyes or colorants when making a colored object.
Different channels may supply different liquid compositions; e.g., different types of material, dyes, and other additives. The powder dispensing device preferably is also capable of depositing solid particles of variable compositions. Such a device, therefore, may also be multi-channeled.
In another embodiment, a process is disclosed which comprises the above three steps, (a) through (c), wherein the moving step includes the steps of (i) moving the deposition sub-system and the platform relative to each other in a direction parallel to the X-Y plane to form a first layer of the deposition materials on the platform; (ii) moving the deposition sub-system and the platform away from one another by a predetermined layer thickness; and (iii) after the portion of the first layer adjacent to the nozzles of the deposition sub-system has solidified, dispensing a second layer of the deposition materials onto the first layer while simultaneously moving the platform and the deposition sub-system relative to each other in a direction parallel to the X-Y plane, whereby the liquid droplets in the second layer solidifies and adheres to the first layer.
In yet another embodiment, a process is disclosed which comprises the above steps, (a) through (c) including (i) through (iii), and additional steps of (e) forming multiple layers of the deposition materials on top of one another by repeated dispensing of the liquid droplets and powder particles from the deposition devices as the platform and the deposition sub-system are moved relative to each other in a direction parallel to the X-Y plane, with the deposition sub-system and the platform being moved away from one another in the Z-direction by a predetermined layer thickness after each preceding layer has been formed, and with the dispensing of each successive layer being controlled to take place after the liquid material in the preceding layer immediately adjacent the deposition sub-system has substantially solidified.
As a further preferred embodiment, the above cited steps (a) through (c) are further combined with the steps of (f) creating an image of the three-dimensional object on a computer with the image including a plurality of segments defining the object; (g) generating programmed signals corresponding to each of the segments in a predetermined sequence; and (h) moving the deposition sub-system and the platform relative to each other in response to the programmed signals. To build a colorful object, each segment is preferably attached with a color code that can be converted to programmed signals for activating the ejection of selected ink-containing liquid compositions to form the desired color pattern of the finished object. Further preferably, the supporting software programs in the computer comprise means for evaluating the CAD data files of the object to locate any un-supported feature of the object and means for defining a support structure for the un-supported feature. The software is also capable of creating a plurality of segments defining the support structure and generating programmed signals required by the same deposition device or a separate fabrication tool to fabricate the support structure.
As another preferred embodiment, the surface areas (exterior regions) of an object are built primarily by the deposition of very fine solidifiable liquid droplets for improved accuracy while the interior regions are built by a mixture of solid powder particles and liquid droplets for improved build speeds. Where needed, the liquid droplets and the solid powder particles are directed to impact substantially the same spots either concurrently or sequentially. Liquid droplets serve the primary purpose of bonding solid particles together to build the bulk of the object, particularly the interior regions. Improved build speeds are achieved through (A) increased over-all material volume flow rates when both liquid droplet ejection device and solid powder dispensing device are operated simultaneously and (B) reduced times for individual layers to solidify to a substantial extent. This latter notion of reduced times is due to the solid particles present being able to cut down the amount of liquid that needs to be solidified. For instance, the core of a large volume of liquid is known to solidify at a lower rate than do the outer regions due to poorer heat transfer. With the presence of fine solid particles, liquid droplets will spread up to occupy thin inter-particle areas and will be able to solidify more rapidly. Additionally, the mere presence of solid particles makes the solid-liquid mixture more viscous or solid-like to begin with so that the over-all time that the deposition device has to wait before starting a next layer is effectively reduced.
The above-cited multiple-channel liquid droplet deposition device may simply be a plurality of separate droplet deposition devices with each device being supplied with possibly different liquid compositions containing different colorants and being capable of ejecting the liquid compositions in the form of droplets on demand. One device or channel may be employed to deposit droplets of a baseline body-building material with other devices being responsible for depositing droplets of selected color inks. Alternatively, each device may be used to deposit a mixture of a baseline material and a selected colorant.
The Apparatus
One embodiment of this invention is an apparatus comprising a material deposition sub-system, an object-supporting platform, and motion devices. The material deposition sub-system is composed of two major components: a liquid droplet deposition device and a powder-dispensing device. The liquid droplet deposition device comprises (1) a multiplicity of flow channels with each channel being supplied with a solidifiable liquid composition, (2) at least one nozzle having a fluid passage in flow communication with one corresponding channel and a discharge orifice, and (3) actuator means located in control relation to these channels for activating droplet ejection through these discharge orifices. The powder-dispensing device comprises (1) at least a flow channel being supplied with solid powder particles, (2) for each flow channel, at least one nozzle having a flow passage in flow communication with the flow channel and a discharge orifice, and (3) valve means located in control relation with corresponding flow channel.
The object-supporting platform is generally flat and is located in close, working proximity to the discharge orifices of the deposition sub-system to receive discharged materials therefrom. The motion devices are coupled to the platform and the material deposition sub-system for moving the deposition sub-system and the platform relative to one another in an X-Y plane defined by first and second directions (X and Y directions) and in a third direction (Z-direction)) orthogonal to the X-Y plane to deposit the liquid droplets and/or solid powder particles to form a three-dimensional object. The motion devices are preferably controlled by a computer system for positioning the deposition sub-system with respect to the platform in accordance with a CAD-generated data file representing the object. Further preferably, the same computer is used to regulate the operations of the material deposition sub-system in such a fashion that liquid droplets and powder particles are dispensed in predetermined sequences and at predetermined proportions.
Specifically, the motion devices are responsive to a CAD-defined data file which is created to represent the 3-D object to be built. An image of the object is first created in a CAD computer. The image is then sectioned into a desired number of layers with each layer being comprised of a plurality of segments represented by a collection of data points. These layer data are then converted to machine control languages that can be used to drive the operation of the functional components, including motion devices. These motion devices operate to provide relative translational motion of the material depositing sub-system with respect to the object platform in a horizontal direction within the X-Y plane. The motion devices further provide relative movements vertically in the Z-direction, each time by a predetermined layer thickness.
The material in each supply of liquid composition may be comprised of, but is not limited to, one or more of the following materials including various adhesives, waxes, thermoplastic polymers, thermosetting resins, metallic alloys, glasses, ceramics, sol-gel mixtures, and combinations thereof. The material may also include combinations containing dissimilar materials added to impart a desired electrical, structural, or other functional characteristic to the material. For making colored objects, preferably each composition also contains a color-making ingredient (referred to as a colorant or ink), which may be a dye, pigment, color concentrate (commonly used in coloring of plastics), or combinations thereof.
One presently preferred liquid composition comprises a hot melt adhesive that exhibits a high adhesion to previously deposited material. The hot melt adhesive also exhibits good mixing characteristics with a variety of colorants. Another preferred material composition comprises fine ceramic, metallic, or polymeric particles dispersed at a high volume content in a liquid (e.g., water) to make a paste. The composition in a paste form normally will not require heating to become a flowable state. In the cases where the liquid content is high, the part-building zone surrounding the platform may be pre-cooled to below the freezing temperature so that the discharged material can rapidly become solidified when in contact with a previous layer or a surface of the platform. A facilitated sublimation procedure may be followed to complete a xe2x80x9cfreeze-dryingxe2x80x9d process. Yet another preferred material composition comprises fine ceramic, metallic, or polymeric particles dispersed in a fast vaporizing liquid to make a paste. The liquid may rapidly vaporize, optionally under the assistance of a vacuum pump, to become solidified upon contact with a previous layer or a surface of the platform.
The solid powders may also be selected from a wide variety of material types, including polymer, metal, glass, ceramic, and combinations thereof. In one embodiment, the liquid droplets are small in size (e.g., 15 xcexcm in diameter or smaller) while the powder particles may be larger in size. The areas near a surface of a part, referred to as the exterior of a part, are preferably built mainly with liquid droplets for improved part accuracy. To achieve a higher build speed, the interior of the part may be built mainly with solid particles which are glued together with a liquid composition. Liquid droplets and solid particles may be deposited concurrently or in sequence. Preferably, liquid compositions and solid particles are chemically compatible so that they can be well bonded together. In the case of co-deposited polymer liquid and polymer powder, the liquid polymer and the solid polymer may be of substantially identical chemical composition; e.g., PVC particles adhered together by PVC melt.
In one embodiment, the droplet deposition device is similar to a multi-channel print-head commonly used in an ink jet printer. The print-head is preferably equipped with heating means to maintain the colorant-carrying material compositions in a liquid state. Ink jet print-heads can generally be divided into two types: one type using thermal energy to produce a vapor bubble in an ink-filled channel that expels a drop of liquid while a second type using a piezoelectric transducer to produce a pressure pulse that expels a droplet from a nozzle. Droplets are dispensed through an orifice to deposit onto predetermined regions of a surface upon which a layer is being built.
In one preferred embodiment, one of the liquid channels may be employed to deliver and deposit a baseline material (e.g., a plastic melt or plastic-liquid paste) that will become the primary constituent material in the object. Such a baseline material is also referred to as a primary body-building material. A selected color ink is then deposited onto this baseline material to create a desired color at a desired spot. Alternatively, the droplets of the baseline material may be deposited simultaneously with the droplets of a color ink dispensed from a different channel. Different parts of a layer and different layers of an object may be built to show different colors.
Advantages of the Invention
The process and apparatus of this invention have several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention as expressed by the claims which follow, its more prominent features will now be discussed briefly. After considering this brief discussion, and particularly after reading the section entitled xe2x80x9cDESCRIPTION OF THE PREFERRED EMBODIMENTSxe2x80x9d one will understand how the features of this invention offer its advantages, which include:
(1) The present invention provides a unique and novel method for producing a three-dimensional object on a layer-by-layer basis under the control of a computer. This method offers an opportunity to impart desirable color patterns to an object, making a form model much more attractive. Both speed and accuracy, which are normally considered to be mutually exclusive in a layer manufacturing technique, can be achieved with the present method.
(2) Most of the layer manufacturing methods, including powder-based techniques such as 3-D printing (3DP) and selective laser sintering (SLS), are normally limited to the fabrication of an object with a uniform material composition. In contrast, the presently invented process readily allows the fabrication of an object having a spatially controlled material composition comprising two or more distinct types of material.
(3) The presently invented method provides a computer-controlled process which places minimal constraint on the variety of materials that can be processed. In the present method, the liquid composition and the solid powder may be selected from a broad array of materials including various organic and inorganic substances and their composites.
(4) The present method provides an adaptive layer-slicing approach and a thickness sensor to allow for in-process correction of any layer thickness variation. The present invention, therefore, offers a preferred method of layer manufacturing when part accuracy is a desirable feature.
(5) In one variation of the presently invented method, fabricated objects may not be permanently fixed (if so desired), but can be easily separated at any one or more of many inter-layer interfaces. The resulting sections can then be easily rejoined to form again the complete object. The object can be thus separated and rejoined at the same or different cross sections, repeatedly and without limitation. Potential applications of forming separated layers of a three-dimensional object include the production of custom-made 3-D puzzles (toys). A set of some hundreds of plastic sheets, when stacked together in the right order, will make a predetermined shape (thus completing a puzzle).
(6) The method can be embodied using simple and inexpensive mechanisms, so that the fabricator equipment can be relatively small, light, inexpensive and easy to maintain.